LW10: Diagnostic tests and screening
LW11: How things can go wrong
LW10
LW11
A company that has produced a new rapid antigen test to detect Covid-19 needs to demonstrate that it has sufficient sensitivity and specificity to pass regulatory requirements.
They conduct a study comparing the RAT outcomes to a real-time reverse-transcription polymerase chain reaction (rRT-PCR) test.
100 people with symptoms of respiratory tract infection are enrolled, 15 people are identified as Covid-positive via rRT-PCR. Of these 15 people, 14 are identified as Covid-positive according to the RAT. Three people with a negative rRT-PCR test were identified as positive according to the RAT.
Determine the sensitivity and specificity of the RAT test and the prevalence of Covid in this sample.
| Condition | No condition | Total | |
|---|---|---|---|
| Test \(+\) | 14 | 3 | 17 |
| Test \(-\) | 1 | 82 | 83 |
| Total | 15 | 85 | 100 |
\(Sn = \frac{a}{a + c} = 14/15= 93\%\)
\(Sp = \frac{d}{b + d} = 82/85 = 96\%\)
\(P = \frac{a + c}{a + b + c + d} = 15/100 = 15\%\)
Predict what will happen to the positive predictive value and negative predictive value of the test if the prevalence of Covid in the community changes.
| Condition | No condition | Total | |
|---|---|---|---|
| Test \(+\) | \(a\) | \(b\) | \(a + b\) |
| Test \(-\) | \(c\) | \(d\) | \(c + d\) |
| Total | \(a + c\) | \(b + d\) | \(a + b + c + d\) |
Review the information provided by Harding Centre for Risk Literacy (below).
Describe ways that the pharmaceutical industry can undermine evidence-based medicine
What tools are available to identify and/or mitigate these attempts?
Explain the subgroup problem.
| Participants | People over 45 with BMI > 27 and established cardiocascular disease and NOT a diagnosis of diabetes |
| Intervention | Semaglutide sc once-weekly (escalating dose to 2.4 mg) |
| Comparator | Placebo |
| Outcome | Composite: Death from cardiovascular disease, nonfatal MI, nonfatal stroke |
The trial included 17 604 participants and the sample was ~ 72% male and 84% white
Explain the following table: